1. Field of the Invention
This invention relates generally to the generation of power from gasified solid fuels such as coal or biomass. More particularly, the present invention relates to an improved power generation cycle for gasified solid fuels that eliminates the need for a high-temperature particulate control system or a wet clean-up scrubbing system.
2. Description of the Related Art
Advanced solid fuel-based power generating cycles include advanced pulverized coal combustion with both direct cycles including integrated gasification combined cycles (IGCC), second-generation or advanced pressurized fluidized-bed combustion (APFBC) cycles, gasification molten carbonate fuel cell (MCFC) cycles, etc. as well as indirect cycles. While all these cycles have the potential to provide cost effective and environmentally benign power generation for needs of utility and industrial sectors, all of these cycles suffer from one common deficiency.
Specifically, all of these cycles produce high-temperature gas streams with unacceptably high particulate and hazardous air pollutants (HAPS) concentrations. In order to utilize the above solid-fuel cycles and meet the environmental standards set by federal and local regulatory bodies, significant advances must be made in the art of removing particulates and HAPs from the high temperature gas streams because both primary methods of removing the particulates and HAPs that are currently available, i.e. (1) currently available high temperature particulate control technology and (2) wet scrubbing systems, are unacceptable for the reasons stated below.
By way of background, APFBC and IGCC systems utilize gas turbines to generate power and therefore any particulates should be removed from the combustion gas upstream of the turbine because excessive levels of particulates in the combustion gas stream will engage the turbine, cause erosion of the turbine blades and result in particulate deposits in the turbine. The result is physical damage to the turbine blades and reduced efficiency of the turbine. Accordingly, the particulates must be removed from the contaminated combustion gas upstream of the turbine in order to protect the turbine and provide acceptable turbine life and efficiency.
Similarly, in an MCFC system, it is important to remove the particulates from the combustion gas upstream of fuel cell because particulates in the combustion gas stream will result in particulate deposits on the small pores of the support structure of the anode which will eventually lead to plugging of these pores. Any plugging of the pores of the support structure will not only damage the support structure but will also result in inefficient operation of the cell.
In solid fuel power generation cycles, high temperature combustion gas streams are required to achieve high cycle efficiency. These temperatures typically should exceed 1100.degree. C. in direct and 1370.degree. C. in indirect cycles. However, at the present time, the ability to operate high-temperature particulate control systems to remove particulates from the high temperature gas streams at these temperatures is quite problematic because the high-temperature particulate control technology currently available for advanced gasification cycles is expensive and unreliable.
Further, there is an additional factor making the high-temperature particulate control unattractive. High-temperature particulate collectors do not usually eliminate the need for additional air toxics control devices because most of the hazardous air pollutants (HAPs) have relatively low boiling points and cannot be effectively controlled by high-temperature particulate collectors.
The problems associated with high-temperature particulate control are not effectively circumvented in a power generating gasification cycle using a wet clean-up process. In a wet clean-up process, the high-temperature gas stream is cooled in a heat recuperator or regenerator and then cleaned with a wet scrubbing system. However, wet scrubbing systems require the injection of large amounts of cleaning liquid (normally water) into the gas stream. Because the added water cools the gas to a temperature below the water condensation temperature, the clean gas therefore contains substantial amounts of moisture by the time it is returned to the heat recuperator or regenerator which results in a very inefficient cycle. Further, wet clean-up systems have high capital cost requirements.
Accordingly, it would be highly desirable to provide a new power generating gasification cycle that could avoid the following problematic solutions taught by the prior art, namely: (1) a high-temperature particulate control systems, and (2) a wet clean-up systems. The present invention provides a solution with a combined power generating gasification cycle that does not resort to the prior art designs discussed above and which further provides a power generation cycle with low space and cost requirements, universal applications, low emission levels and high cycle efficiency.